1. Field of the Invention
The present invention relates to an LED driver circuit, and more particularly to a driver circuit with a primary side regulating architecture and a two-stage isolation transformer for improving LED flickers.
2. Description of the Related Art
In a conventional LED driver circuit, a single-stage flyback LED driver circuit architecture is generally adopted, wherein the voltage at an input terminal and the conversion of voltage by a transformer are provided for achieving the effect of driving an LED. When the power is turned on, electric energy is converted into magnetic energy stored in the transformer, and when the power is turned off, the magnetic energy in the transformer is converted into electric energy which is discharged to a secondary side, such that a buffer capacitor of the secondary side moderates the output voltage to drive the LED. However, the single-stage flyback LED driver circuit has a relatively too-high ripple voltage outputted from the secondary side, and the output current is not a constant current, so that the LED produces flickers. To improve and eliminate the flickers, it is necessary to increase the capacitance value of the buffer capacitor, and the increase of this numeric value reduces the power factor and increases the cost of the overall circuit.
In addition, the feedback of a secondary side optocoupler used as the method of the LED driver circuit is proposed, and the optocoupler has the effect of isolating the high pressure of the primary side and the low pressure of the secondary side, and generating and transmitting a feedback signal from the secondary side to the primary side to regulate the current, so as to achieve the effects of maintaining a constant current and improving the issue of LED flickers effectively. However, the method of using the feedback of the optocoupler as the LED driver circuit is relatively more complicated, and this method also requires a larger space of the circuit board and incurs a high component cost. The power factor is calculated by multiplying those of the primary side and the secondary side together, so that it is difficult to improve the overall efficiency of the circuit.
Therefore, the present invention provides a driver circuit for improving LED flickers, and the driver circuit is applied to a panel light, wherein the driver circuit uses a two-stage isolation transformer and a primary side regulating circuit, without requiring the use of the optocoupler for the feedback control or increasing the level of difficulty of the circuit, so as to achieve a better circuit efficiency and use less components. When a PWM dimming signal of 1V-10V is inputted, the issue of flickers of the LED driver circuit is improved effectively.